(1) Field of the Invention
The present invention relates generally to sewage treatment and more particularly to septic tank sewage treatment systems. More particularly still, the invention relates broadly to filtering the effluent from a septic tank system and to a filter arrangement and method for filtering septic tank discharge prior to passage of such effluent to a drain field or other ground disposal system to prevent clogging or plugging of such drain field or system.
(2) Description of the Prior Art
Municipal treatment systems usually comprise widespread pipe collection systems capped by large scale treatment facilities including settling, coarse and fine filtering and possible other treatments, denoted usually as primary, secondary and, less frequently, tertiary treatment of the sewage. Not unexpectedly, private sewage treatment systems are usually relatively more simple. One of the most widespread presently used private treatment arrangements involves the use of septic holding tanks in which solids originally discharged from a waste source with the liquid portion of the sewage or waste are allowed to settle in a large tank or tanks. The overflow from the septic tank is directed into either a so-called dry well from which it percolates into the ground, where passage through rock and ground strata further purifies the waste water and removes harmful bacteria and other noxious components, or into a so-called drain field comprised of a series of perforated ceramic pipes or drains laid into shallow trenches in the ground from which the liquid portion of the sewage is absorbed or percolates into the ground where it is likewise purified by passage through the ground strata.
With the widespread exodus from city environments to suburban and semirural environments, the use of septic systems, so called because of the use of a "septic tank" into which septic or bacteria-laden liquid and included solid or semisolid materials are discharged for temporary holding and settling of the solids from the liquid material discharged into the tank, has been growing at a rapid rate. Such widespread use of septic tank systems results from the fact that only a limited number of suburban and substantially no rural areas have municipal or public sewage collection and treatment systems. Other individual treatment systems such as basic cesspools or holding tanks, dry systems and the like are also available, but none has become popular because of various problems, expenses and other inconveniences. Consequently, while the trend for some years in the past was away from the use of the "septic" and other localized or private sewage treatment arrangements, as cities and large towns converted their residents' sewage disposal systems from private systems to large public systems, with the recent exodus of city residents to suburban and semirural environments surrounding most cities beginning soon after the second world war the trend to municipal systems has substantially reversed. Septic-type systems are presently growing apace. Furthermore, with the burgeoning suburban and semirural population and the increasing environmental consciousness of such population, efficient and effective sewage treatment on a small scale within the confines of a residential property or small business or industrial environment has assumed more and more importance.
Typically the overflow from a septic tank passes first into a distribution box before it is distributed into a drain field. The well regulated septic tank may ordinarily discharge suspended solids in an amount of about 125 to 175 parts per million of the effluent waste water after it leaves the septic or sewage tank, although this will vary depending upon the amount of flow from the tank and other factors including the level of solids maintained or accumulated in the bottom of the tank. The amount of suspended solids in the supernatent liquid tends to increase or decrease in inverse ratio with distance from the accumulated solids at the bottom of the septic tank. When the solids reach an unacceptable level in the tank, an excessive amount of solids tends to be discharged with the effluent. Consequently, when the level of solids becomes too high or the rate of included solid overflow excessive, the tank must be "pumped" or discharged into a tank truck and the contents disposed of. Various schemes for deciding when the amount of solids passing to the drain field is excessive have been devised, including the use of filters to catch the solids and estimate how much is escaping into the drain field. The escape of solids into a drain field is highly undesirable because it tends to clog up such drain field, which, when clogged, is almost impossible to unclog and must usually be replaced at considerable expense. In order to get penetration of the effluent into the drain field pipe, it is desirable that the overflow vary in intensity so that it will flow through the pipe towards its end and be distributed along the length of the pipe rather than all stopping at one point possibly quickly clogging the system at that point. So-called "dribble systems" in which the sewage overflows or continuously flows in a "dribble" into the drain field are usually not favored, but instead, the effluent is preferably "dosed" into the field with a slight "head" or force behind the flow. It is difficult to arrange for reliable alternating flow, however, particularly as the flow rate by the time it has been distributed into a large drain field may be very low.
The drain field trenches, which typically comprise a trench having a depth of about 2 to 3 feet and two-and-a-half feet in width in which a ceramic pipe having perforations or openings therein of about one-half inch in diameter is laid, are filled usually with gravel or crushed rock and covered over by soil and back filled to grade level. Some systems involve only a single trench leaving room for later adjacent construction of additional trenches when the first drain field pipe eventually clogs. Other systems can include a series of trenches with provision to switch the effluent from one to another via a distribution junction box to prevent saturation of any one trench. The drain trenches in these systems are provided with time between "dosings" to regenerate by decomposing and generally disposing of liquids and small solid particulates between use. Since a drain field is normally continuously receiving a small amount of overflow solids from its disposal or waste tank, which is usually in the form of a septic tank, and the internal spaces of the drain pipes and external surrounding spaces within the trench cannot expand, the drain field must inevitably become too clogged to continue in operation and must be shut down and replaced. Such inevitable shutdown can be delayed by proper operation of the system to either (a) prevent as much as possible the escape of solid materials into the drain field and/or (b) by increasing the decomposition of the solids within the drain field to encourage liquefaction of the solid materials into a form that can be flushed away. It has been reported in some cases, in fact, that it is desirable to have very small particulates escape into the drain field as this tends to provide general decomposition therein, actually tending to decrease or even reverse solid buildup.
In recent years the use of so-called sand mounds has become popular or even mandated in some areas. Sand mounds, as indicated by the name, are mounds of sand placed upon the normal surface of the ground. Smaller than normal drain pipes are incorporated into such mounds. The drain pipes are usually one-and-one-half inches in diameter and have three-sixteenth inch drain openings spaced at about six-foot intervals. The pipes are surrounded by crushed rock placed upon varying depths of sand and the entire mound is then covered with soil and planted or landscaped. The septic effluent is frequently pumped to the sand mound because of its higher surface location with respect to the usual location of a septic tank. The pump is normally run intermittently in order to dose the drains and obtain better liquid penetration. Also a cleanout pipe or connection is frequently provided at the top of the mound. This pipe may be connected to a hose to flush out the drain field pipe or pipes. While the pipes are usually, in fact, flushed out, unfortunately the pipe orifices as well as the drain field frequently remain largely or partially blocked. In fact, the flushing itself may serve to force solid particulates compactly into the sand mound reducing its permiability.
It has been recognized that it might be advantageous to filter solid material from the overflow from a septic tank system (a) to decrease, or even completely eliminate, the usual small amount of solids passing to the drain field and/or (b) to prevent the escape of too large an amount of solids from the septic tank to the drain field during excess flow from the septic tank or (c) to prevent the escape of solids to the drain field as a result of excess buildup of solids in the septic tank. While attractive in theory, such filter arrangements have largely not proved to be practical or effective in preventing the clogging of drain fields. This has been because the filter either interferred with the normal flow of liquid effluent to the drain field, was not easily replaced, did not effectively filter very small particles from the effluent liquid or was impractically complicated or expensive.
Among the more notable proposals for the use of filters to strain or treat the overflow from a septic tank are the disclosures of the following patents:
U.S. Pat. No. 1,454,723 issued May 8, 1923 to W. T. Burtis broadly discloses the use of a filter arrangement with a septic tank system. A removable filter is comprised of a removable basket filled with alternate layers of sand and gravel to effect initial filtering of waste water received from a cesspool, septic tank or grease trap. The filtering system in the Burtis arrangement is not located between a cesspool and a drain field, but is located at the end of the system over a dry well into which the effluent is discharged.
U.S. Pat. No. 3,332,552 issued Jul. 25, 1967 to R. L. Zabel discloses a filter for placement directly in a septic tank. The filter is attached to the overflow from such septic tank and is made in a tubular shape with a series of dam and weir units in a stacked arrangement. The inlet to the septic tank is in a T-shape conducting the liquid to a lower portion of the tank about at the level of the bottom of the dam and weir filter arrangement at the overflow side of the septic tank.
U.S. Pat. No. 3,460,675 issued Aug. 12, 1969 to R. M. Hicks et al. discloses a septic tank inspection arrangement. Hicks discloses that it is desirable to prevent solid material from escaping from the septic tank and penetrating into the leach or drain field area, stopping up the leach field and destroying the operation of the field. Hicks provides a separate trap between the septic tank and the drain field into which solid materials tend to flow and are collected in a receptacle in the trap. The receptacle is provided with a handle which extends to the surface of the trap and after removal of a cover, the receptacle can be lifted up and examined to determine how much solid material is flowing from the septic tank to the drain field or into the trap. If no solids are collected in the trap, the homeowner knows that none are flowing to the drain field, while if there are solids in the trap, he knows that some may be flowing to the drain field and that the septic tank should be cleaned to lower the level of solids before the drain field is plugged up and ruined. The trap is in the form of a removable bucket or container rather than a filter. Since the test applied is qualitative rather than quantitative it is not important that all solids are not caught.
U.S. Pat. No. 3,642,138 issued Feb. 15, 1972 to R. F. Sheda discloses a filtering tank for use with a septic system. The filtering tank has an inlet and an outlet and a series of filters formed from, for example, chopped spagnum moss as a natural filtering material. The moss is retained in cages which may be lowered by a hook into position in the bottom of the filtering chamber. A removable insulation panel is also disclosed across the top of the filter units to prevent the filtering unit from becoming too warm during hot weather.
U.S. Pat. No. 4,104,166 issued Aug. 1, 1978 to J. LaRaus discloses a purification tank which may be used between a septic tank and a drain field. The purification tank in which the sewage or effluent from the septic tank is treated with oxygen or ozone includes a multi-part filter in the bottom through which the material flows or is pumped to the drain field. The filter is provided with a bail on the top so that it may be removed by means of a hook from the surface by opening the top of the purification chamber. There is also an arrangement for backwashing the filter if necessary. The filter has a screen on the bottom over which there is a layer of peat gravel, covered by a layer of anthrofil, or granulated coal, with a surmounting layer of the fine sand. Other filter arrangements may be used. It is said that the filtered fluid is so clear that it may be used for certain low-grade purposes such as irrigation, toilet use, lawn sprinkling or the like. It is also stated that because the cleaned effluent contains no solids, it requires a smaller leach field than the ordinary septic tank system. The filter is removed for cleaning or replacement periodically as it becomes contaminated.
U.S. Pat. No. 4,319,998 issued Mar. 16, 1982 to J. D. Anderson discloses a monitor for an effluent system used between a septic tank and a disposal field. A separate monitor chamber is provided between the septic tank and the field in which there is a screen. The screen is arranged in the monitor chamber with a vertical orientation so that when the screen is clean, liquid flows through it unobstructed while when the screen becomes partially occluded by solid materials, the liquid backs up on the feed side of the screen. A suitable detector is arranged to detect any such backup of liquid, thus warning that the screen has become clogged due presumably to an excessive of solid materials overflowing from the septic tank. This then, in effect, warns the user that the septic tank should be cleaned.
U.S. Pat. No. 4,439,323 issued Mar. 27, 1984 to H. L. Ball discloses a method for filtering waste water from a septic tank. Ball discloses that mechanical filtering devices placed within septic tanks have generally been unsuccessful because the filter quickly became clogged by the solids present in the tank. Various expedients for avoiding such clogging have been used. Ball provides a hollow screen within a housing within the septic tank with the inlet arranged in the area of relatively particle-free liquid. The filter is also protected from solid materials floating on the surface of the water by the external wall of the filter chamber within the septic tank. The result is that Ball is able to use a large filter area with a feed taken from a fairly restricted level within the septic tank within which few solids are found which might otherwise tend to quickly clog up the filter.
U.S. Pat. No. 4,614,584 issued Sep. 30, 1986 to M. B. Di Duca discloses a distribution box for a drain field receiving effluent from a septic tank. The distribution box is provided with a horizontal screen through which the effluent from the septic tank seeps downwardly and is directed through suitable piping to the drain field. The filter screen, which is basically a flat horizontal perforated plate or screen, has handles so that it may be conveniently lifted from the distribution box when the top of the box is removed for cleaning and the like.
U.S. Pat. No. 4,710,295 issued Dec. 1, 1987 to R. Zabel discloses a septic tank filter basically similar to the earlier Zabel filter disclosed in his U.S. Pat. No. 3,332,552. The improvement includes a bottom cone arrangement on the filter unit which tends to collect solid materials and allow them to escape through a hole in the bottom of the conical bottom cap where they collect on the bottom of the septic tank.
U.S. Pat. No. 4,882,045 issued Nov. 21, 1989 to R. J. Bergh et al. discloses a selective distribution to various selected drainage field trenches making use of a special distribution box. The distribution box enables an operator to change the distribution from one drainage field trench to another when a first trench becomes saturated. Along with the distribution arrangement, Bergh et al. uses a filter arrangement on his distribution unit which filter arrangement prevents excess solids from passing from the septic or sewage tank to the drain field trenches. The core of the distribution unit can be removed together with the filter from the top for cleaning. Bergh et al. also discloses the use of a sensor within the distribution box to determine when the unit may be clogged.
While some of the foregoing patents may disclose operative filter arrangements for filtering the effluent from a septic tank before it is distributed to a drain field for further treatment and disposal, none has proved to be the simple, effective arrangement which is required to prevent drain fields from becoming clogged. In general, the filters of the prior art have either been inefficient, too difficult to change or interfere with dosing of the drain field system. The filters, furthermore, have themselves clogged too easily and quickly. The present inventor has unexpectedly discovered and developed, by careful testing and experimentation, a filter and filter arrangement which largely obviates the various defects of the previous arrangements.